48RE Automatic Transmission - Diesel

P0974-TRANSMISSION OVERDRIVE CIRCUIT VOLTAGE TOO HIGH (DIESEL)

For a complete wiring diagram refer to Diagrams/Electrical. Electrical Diagrams

Theory of Operation

The 3-4 Solenoid is used the engage the gear change from 3rd gear to 4th gear.

The solenoids used in transmission applications are attached to valves which can be classified as normally open or normally closed. The normally open solenoid valve is defined as a valve which allows hydraulic flow when no current or voltage is applied to the solenoid. The normally closed solenoid valve is defined as a valve which does not allow hydraulic flow when no current or voltage is applied to the solenoid. These valves perform hydraulic control functions for the transmission and must therefore be durable and tolerant of dirt particles. For these reasons, the valves have hardened steel poppets and ball valves. The solenoids operate the valves directly, which means that the solenoids must have very high outputs to close the valves against the sizable flow areas and line pressures found in current transmissions. Fast response time is also necessary to ensure accurate control.

- When Monitored:

Continuously with ignition on.

- Set Condition:

This code will set if the voltage detected on the 3-4 Shift Solenoid Control circuit at the ECM is different then the expected voltage. Note: To clear this DTC it is necessary to drive the vehicle at a sustained speed which would allow the TCC and/or Overdrive Clutch to operate

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Checkout (Diesel)

Diagnostic Test

1. CHECK IF ANY TRANSMISSION CONTROL DTCS ARE PRESENT

Ignition on, engine not running.

With the scan tool, read Engine DTCs.

Are there any Transmission Control DTC's present?

Yes

- Refer to the Transmission category and perform the appropriate symptom(s).

No

- Go To 2

2. CHECK IF THE DTC IS CURRENT

Ignition on, engine not running.

With the scan tool, read Engine DTCs.

Record the Freeze Frame data for the reported DTC.

With the scan tool, erase DTCs.

Turn the ignition off to the lock position.

Using the Freeze Frame data recorded earlier, try to duplicate the conditions in which the DTC originally set.

NOTE: It may be necessary to road test the vehicle to duplicate the original set conditions.

With the scan tool, read Engine DTCs.

Did the DTC reset?

Yes

- Go To 3

No

- Go To 7

3. CHECK THE 3-4 SOLENOID

Turn the ignition off to the lock position.

Disconnect the ECM harness connectors.

Ignition on, engine not running.

Measure the voltage of the (T9) 3-4 Solenoid Control circuit.

Is the voltage above 0.5 volts?

Yes

- Repair the (T9) 3-4 Solenoid Control circuit for a short to voltage.
- Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Transmission Verification Test

No

- Go To 5

5. CHECK THE (T9) 3-4 SHIFT SOLENOID CONTROL CIRCUIT FOR A SHORT TO ANOTHER CIRCUIT

Turn the ignition off to the lock position.

Disconnect the ECM C1 and C2 harness connectors.

Disconnect the Transmission Solenoid Assembly harness connector.

Remove the Transmission Control Relay.

Measure the resistance between the (T9) 3-4 Shift Solenoid Control circuit and all other circuits in the Transmission Solenoid Assembly harness connector.

Is the resistance below 5.0 ohms between the (T9) 3-4 Shift Solenoid Control circuit and any other circuit(s) in the ECM C1 and C2 harness connectors?

Yes

- Repair the 3-4 Shift Solenoid Control circuit for a short to another circuit(s).
- Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Transmission Verification Test

No

- Go To 6

6. CHECK THE 3-4 SOLENOID

Turn the ignition off to the lock position.

Disconnect the Transmission Solenoid Assembly harness connector.

Ignition on, engine not running.

With the scan tool, actuate the 3-4 (Overdrive) Solenoid.

Using a 12-volt test light connected to 12-volts, check the 3-4 Solenoid Control circuit in the Transmission Solenoid Assembly harness connector.

NOTE: The test light must illuminate brightly. Compare the brightness to that of a direct connection to the battery.

Does the test light cycle on and off and illuminate brightly?

Yes

- Go To 7

No

- Using the schematics as a guide, check the Engine Control Module (ECM) pins, terminals, and connectors for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace and program the ECM.
- Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Transmission Verification Test

7. INTERMITTENT WIRING AND CONNECTORS

The conditions necessary set this DTC are not present at this time.

Use the Freeze Frame Data to help duplicate the conditions that set the DTC. Pay particular attention to the DTC set conditions, such as, VSS, MAP, ECT, and Load.

Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires.

Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.

Refer to any technical service bulletins that may apply.

Were there any problems found?

Yes

- Repair as necessary.
- Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Transmission Verification Test

No

- Test Complete.